Image intensifier tubes (also known as IIT or image intensifiers) are widely used for sensing and amplifying, or intensifying, light images of low intensity. In these devices, light (usually of visible or near infra-red spectra) from an associated optical system is directed onto a photocathode which emits a distribution of photoelectrons in response to the input radiation.
Image intensifier tubes typically include a vacuum tube with a photocathode unit at one end and a screen unit at the other end. The photocathode unit converts incoming photons to electrons which are accelerated by an electric field (potential difference) in the tube until they hit the screen unit converting them back to photons.
Image intensifiers are used in various imaging and inspection systems, including those used in the semiconductor industry for manufacturing integrated circuits. In such systems, an image intensifier is appropriately located in front of an image sensor (e.g. CCD or CMOS camera). Such systems are disclosed for example in U.S. Pat. No. 6,661,508; EP 305644 and US 2005/0219518 all assigned to the assignee of the present application, and U.S. Pat. No. 4,755,874.